J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

ISSN : 2028-2508

CODEN: JMESCN

463

Recovery of Alumina from a surface - Treatment industry

N. Lamarti*, L. Ben Allal, A. Azmani Laboratoire des Matériaux et valorisation des ressources (LMVR), Université Abdelmalek Essaâdi , Faculté des

Sciences et Techniques de Tanger, BP 416 Tanger, Maroc

*Corresponding Author. E-mail: nissrine-lamarti@hotmail.fr

Abstract Surface treatment industries are among the most polluting industries, they generate very basic effluents

containing very high concentrations of metals. Spent liquor from the pickling of dies for the production of

aluminum extrusions with caustic soda has been studied. These effluents are typically dewatered to reduce the

volume of waste before to be land filling. In Europe, it is estimated that about at least 14,000m3 of this residue is

produced per year. The Recovery of alumina is important both environmentally by reducing the amount of

sludge deposited and economically by obtaining alumina. Alumina is a material finding many applications in

catalysis, manufacturing of ceramics, refractory. In recent years, a special attention has been focused on the

preparation of (Al2O3) powders with high purity by various routes such as precipitation, sol-gel and

hydrothermal methods. Among these methods, precipitation is the most commonly used method not only

because it can produce high quality powders but also it is cheap. The precipitation of aluminum depends on

several factors as temperature and pH . In this work the factor studied is the pH at 25°C. The aim of this work is

to reach the point of maximum precipitation of aluminum to recovery the maximum amount of aluminum; the

(H2SO4) is used. The X-ray diffraction and X-ray fluorescence analysis were used to study the characteristics of

alumina and the titration curves are performed in laboratory. The purity of alumina obtained is nearly 60%, the

spectra of alumina showed the presence of alumina in amorphous form.

Keywords: pickling batch-Aluminum hydroxide-precipitation-Alumina

1. Introduction

The extrusion of the aluminum billets [1] is a necessary step for aluminum production. This technology consists

of pushing a hot cylindrical metal billet on within stainless steel die. In order to achieve good quality extruded

products, the internal surfaces of the extrusion dies must be perfectly clean [2]. Pickling is probably one of the

surface treatment operations among the best known. However, pikling term has a different meaning for all

professionals [3].

In this work the meaning of pickling[4] is a cleaning the extrusion dies because after each pickling (one cycle)

the matrixes of extrusions must be dismounted and cleaned to remove aluminum that has remained in the holes

(2 Kg -3Kg Al per die), this step is necessary to ensure perfect quality profiles .This operation (600Kg Al per

cycle) is done by soaking the dies for 7 hours in a concentrated NaOH solution (some 40% by weight) at a

temperature approximately 70 °C[5].

This treatment brings aluminum into the solution as aluminates [5], according to the reaction:

2Al 2 +‏OH‏ −

+ 6 H2O → 2 Al (OH)4‏ −

+ 3H2 (1)

As a consequence, a waste containing high amounts of aluminum is generated. In Europe, it is estimated that

about at least 14,000m3 of this residue is produced per year [6] normally; the pickling solution is treated by

neutralization in the profiling aluminum industry according to the following reaction:

Al(OH)4−→ Al(OH)3 + OH

−(aq) (2)

This method causes a continuous loss of resource materials (aluminum), as well as it results in generation of

very large amounts of solid aluminum hydroxide residues [7] these residues are typically dewatered to reduce

the volume of waste prior to being land filled.

Different works were demonstrated the possibility to recover of alumina from the wastewater of the profiling

industries[8,9].In the work we'll study the possibility of alumina recovery from the waste effluents generated

J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

ISSN : 2028-2508

CODEN: JMESCN

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during the cleaning of the extruder matrixes of the profiling aluminum industry by precipitation method to

solve the pickling bath management.

The first step of experimental method is the dilution, followed by precipitation (maximum precipitation) the

phosphoric acid is adding; the precipitate of aluminum hydroxide is filtered, the last step is calcinations [10, 11]

to recovery of alumina. The method presents both economic (the use of alumina) [12, 13, 14] and environmental

interests [15] and is an easy implanted solution to solve management problems of industrial waste.

2. Experimental 2.1. Materials

A representative sample (at the practical work conditions in the factory) of wastewater resulting from alkali

washing of the extrusion dyes was collected by a Moroccan anodizing factory (Aluminium du Maroc). In the

experimental procedure height purity of sulfuric Acid (H2SO4) and chloridric acid (HCl) is used, the

experiments were realized with the diluted acids. The pH meter and magnetic stirrer were used to precipitation

performed.

2.2 Procedure

2.2 2. Procedure for alumina recovery

The profiling aluminum industry uses a concentrated caustic soda to clean the internal surface of extruder

matrixe to solubilise all aluminum that stood in the dies ,as Al(OH)4−species . Thus the pH of waste water

effluent is very basic (pH=13, 95).

The waste effluent is diluted; the sulfuric acid is added until to maximal precipitation point of alumina.This step

is followed by washing the precipitate with the distilled water and filtration. The last step is the hydroxide

aluminum calcination in the furnace (1200°C), this step is necessary to recovery of alumina.

2.2.3. Principle of aluminum solubility:

Aluminum in the aqueous solutions at 25° is present in three forms Al3+,

Al (OH)3 , Al(OH)4−

depending on the pH value (Figure 1 )The reactions and formulas involved are:

Al (OH)3 (s) --->Al3+

+ 3OH-

Ks1 = [Al3+

][OH -]

3

Al (OH)3 + OH- ---> Al(OH)4

−

Ks2= [Al (OH)4−]

[OH

-]

After developing the formulas we get: 4pH=pKs2+4pKe –pKs1+log3

Figure 1: Speciation of aluminum in aqueous solutions at 25 °C [6]

The theoric pH value corresponding at the maximum precipitation of Al (OH)3 is constant because it does not

depend on aluminum concentration but it only depends on the values of pKe, pKs1, pKs2. These values are

constant for a temperature 25 ° C.

In these experiments, a basic original effluent aluminum is diluted (dilution factor is 3) , the sulfuric acid (2N)

is used to reach the pH value of 5,8(maximal precipitation).The temperature regulation at 25°C is necessary to

keep the values pks1, pKs2, pKe constant.

Precipitation experiments were performed in a glass beaker, a pH meter with automatic recording device to

temperature display is used , a volume of 10ml of effluent is diluted with distilled water 20ml, this solution is

J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

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titrated with H2SO4 (2N) (solutions are used diluted in order to keep the temperature constant 25 °C) with

stirring.

These results are necessary to draw a titration curve of aluminum for obtaining the point of maximum

precipitation and the curve of solubility product Ps depending on the pH: Ps = f (pH).

A comparison between the point of maximum experimental and theoretical precipitation is performed and the

necessary volume of sulfuric acid to decrease the pH to down 5,8 is performed by titration curve and curve

Ps=f(pH).The precipitate (Al (OH)3) is washed by distilled water to eliminate the impurities, this step is

followed by filtration and calcination in a furnace at 1200° during 2h.The characterization of alumina is carried

out by X-ray diffraction (XRD) and X-Fluorescence analysis.

3. Results and discussion 3.1. Chemical characterization of the original effluent

The chemical characterization of original effluent from the profiling aluminum industry is performed by

Spectrometry Atomic Emission ICP AES (Ultima 2 - JobinYvon).

Table 1 shows the total metals (aluminum, chromium, copper, silicon, nickel and Zinc) concentrations present in

the original basic suspension.

The free NaOH concentration is realized by volumetric analysis through titration with H2SO4 (1N), the dissolved

aluminum concentration is carried out by two methods the volumetric analysis H2SO4 (1N) and Atomic

Emission Spectrometry ICP (AES), as well as the pH, temperature and density are determinate in the laboratory

(Table 2). The pH values of all effluent are measured at a constant temperature 25 °C to avoid the change of the

constant pKa.

The results of analysis show Table 1 that aluminum and sodium are the main elements present in the original

effluent. Silicon is also present, as a minor element, and mainly in the colloid form. Copper, chromium nickel,

Zinc are the minor constituents of original effluent.

At pH around 14 aluminum, copper, Zinc and Nickel are totally soluble [9]. In the case of sodium, all the total

amount of sodium present in the wastewater (Table1 ) results from the sodium hydroxide added to the cleaning

bath, the silicon present in the original effluent results from the aluminum alloys billets used in the profiling

industry is (AL-Si 6060) between 0,30 wt.% -0,60 wt.%.

Table 1: Chemical composition of the original effluent

The Table2 summarizes, in particular, the main chemical parameters of the original solution. In the pickling

process The concentration of Aluminum at form Al (OH)4- specie (dissolved aluminum) increases and the

rinsing caustic solution loses its activity .The results of Table2 demonstrate that the concentration of caustic

soda is very high 7,3M and the concentration of aluminum in the effluent is 5,40M so this effluent is very

concentrated and contains important amount of aluminum .

3.2. The Alumina recovery:

The proposed experimental of Alumina recovery is composed by three steps, the first step is a dilution (3

dilution factor) this is step is necessary for reducing the viscosity of basic effluent and the control of temperature

(25°C). The second step is a neutralization of the basic effluent to down pH=5,8 (point of maximum

precipitation) , the sulfuric acid is used because it is the cheapest acid [5] a volume 0,16 ml of concentrated

sulfuric acid (95%) is necessary for decreasing the pH of the basic solution to 5,8 (6ml of H2SO4 (1N) , the

precipitate recovery Al (OH)3 is filtered and washed three times by dezioned water . The final step is the

calcinations of the precipitate in a furnace at 1200° during 2h to recovery the alumina.

Constituent concentration

Al 146 g/l

Si 96,350 mg/l

Cr 0 ,206 mg/l

Ni 0,008 mg/l

Zn 0,623 mg/l

Cu 0,042 mg/l

Na 900g/l

J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

ISSN : 2028-2508

CODEN: JMESCN

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Table2: characterization of the original effluent

3.2.1 Aluminum precipitation:

The titration curve obtained at 25°C is shown in Figure 2, from these curves, three regions are distinguished :

Figure 2: Titration curve obtained at 25°C by addition of H2SO4 (2N)

Region I: (pH between13,42 and 10 ):the pH decrease progressively until the value 10,58,this region is

characterized by the high solubility of Aluminum and the aluminates ion Al (OH4)- dominance .

Region II : (pH between 10 et 4) presence of a bearing, the pH value decreases from 10.58 to 4. This region

represents the region of the lowest aluminum solubility and thus aluminum was massively removed from the

solution, forming initially a very viscous gel due to intense condensation phenomena and then an extremely

viscous pulp consisting principally of an amorphous solid material. The results of experiments obtained in the

laboratory demonstrated than the volume of sulfuric acid causing maximum precipitation (solid gel) is 45 ml,

which corresponds to a pH value of 5.6 Figure 2 , after this volume the addition of sulfuric acid causes a

beginning of redissolution of the precipitate and pH decreasing.

Region III: pH is bellow to 4 the pH starts to decrease and we see the total and net redissolution of the gel

formed, the aluminum hydroxide Al (OH)3 was transformed into Al 3+

.

Curve Ps=f(pH) The concentration of aluminum value of the original effluent allowed us to define the corresponding pH values

of total redissolution in acidic and basic aqueous solution respectively 3.03 and 13.60.

The PH value corresponding a maximal precipitation is not depending of aluminum concentration, this is almost

5, 8 (see precipitation of aluminum part introduction).For a pH value between 3.03 and 5.8 the formula is:

Ps = -9.7 + 3 pH ,and to a pH value between 5.8 and 13.60 is the formula: Ps = 13-pH .The results obtained are

shown in the curve below (Figure3). These results demonstrated than the lower solubility of aluminum is

obtained at pH= 6 ,at this pH the aluminum is present at species form Al(OH)3 (precipitate), this pH value is

almost the pH value of maximal precipitation obtained in the titration curve (Figure2) pH=5,3 .At a pH below

3 the solubility of aluminum is zero, the aluminum is present in its soluble form Al 3+

, this value is nearly the

same value of 3.74 pH obtained in the titration curve (the total redissolution ). The aluminum solubility

decreases to a pH value between 4 and 10 until total redissolution at pH values 3 and 13.

The results obtained by the titration curve (experimental method) are confirmed by the curve Ps = f (pH)

(theoretical method). Thus we can conclude that the pH value corresponding to the point of maximum

precipitation of original effluent is between 5.3 and 6.

0

5

10

15

0 5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10

0

10

5

pH

V(H2SO4) /ml

Titration curve

RegionI RegionII Region III

Parameter value

pH 13 ,70

T° 25°C

Density 1,40

[NaOH] 321g/l

[Al] 146g/l

J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

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Figure 3: The solubility Ps=f (pH)

3, 2.2. Alumina recovery

The characterization of Alumina is performed by XRD patterns and X Fluorescence spectroscopy. The purity of

Alumina obtained by precipitation at 25°C and calcination at 1200°C in furnace during 2h is determined by the

X Fluorescence analysis as shown in Table 3. The result shows that the purity of alumina recovery is almost

60%, the major impurities are the sodium, sulphates and silicates with values respectively 19%, 15,1%,2,14%.

The sodium oxide present (Na2O) as a major element 19% results from the caustic soda added to the clearing

bath by against the value of the sulfide (SO3) 15% results from the sulfuric acid added to produced the maximal

precipitation and the silicon value (SiO2) 2,14 % results from the Aluminum alloy. The silicon is the major

constituent of Aluminum alloy. The content of minor impurity is almost 10% (eg. iron, magnesium, chromium,

nickel), these all elements are constituents of the aluminum alloy (minor constituents of aluminum alloy).

Table 3: Alumina recovery Results by X fluorescence

Element Concentration% Element Concentration%

Al2O3 55,700 Fe2O3 0,196

Na2O 19 Cr2O3 0,059

SO3 15,100 K2O 0,024

SiO2 2,190 NiO 0,024

Mg O 0,494 P2O5 0,018

The XRD diagrams in Figure 4 shows that at a lowest temperature 25°C and for pH =5,3 totally amorphous

phase was formed [8] .The spectrum of alumina resulting is amorphous, this result is explained by the non-

compliance of the calcination temperature (malfunction of the furnace) , The resulting precipitate was calcined

at a temperature of 900 °C instead of 1200 °C, for obtaining the alumina in its crystalline form , the temperature

should be 1200°C.

Fig 4: the Alumina recovery spectrum by rayon X diffraxion

-2

0

2

4

6

8

0 5 10 15

Ps

pH

J. Mater. Environ. Sci. 7 (2) (2016) 463-468 Lamarti et al.

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Conclusion

In this work we were able to recover the alumina from a pickling bath of aluminum alloys by the method of

precipitation at 25 °C.

The comparison between the theoric value of maximal precipitation point of aluminum was confirmed by the

experimental results of titration curves and curve Ps=f(pH),the maximal precipitation point is obtained for pH

value between 5,3 and 6.The X Fluorescence analysis of alumina demonstrated that the purity of alumina

recovery was almost 60%, the spectrum of alumina carried out by rayon X diffraction is amorphous, and these

results can be explained by the low temperature of precipitation [8] or by the non conformity of the calcination

temperature .

The process performed during this study presents both economic (alumina) and environmental interests (setting

discharge of sludge) and is an easy implanted solution to solve management problems of industrial waste. This

method shows how a waste can save money not only by the recovery of alumina but by the elimination of

treatment cost and the alumina recovery can be used as an adsorbent, a catalyst or a refractory material.

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(2016) ; http://www.jmaterenvironsci.com